Mold processes for manufacturing the above type of products with recesses or cells are known. For example, according to a known process, the manufacture of a cellular mattress is effected by employing a mold which opens into two halves and filling the mold partially with latex foam material and allowing the latex foam material to foam when the mold is closed. One or both parts of the mold are provided with a plurality of protuberances which have an overall conical shape or a substantially cylindrical shape with a conical end; these protuberances have a shape corresponding to the recesses or cells of the mattress to be formed. The mold is adequately heated by introducing a liquid at a predetermined temperature for thermal treatment of the article along an appropriate outer hollow space. In a subsequent step, the mold is opened and the mattress must be manually removed from the upper cover since the mattress becomes adhered to the protuberances of the upper cover during the molding process. In succeeding steps, the mattress is washed to remove undesired substances in the finished product and it is then subjected to a drying process.
In another heretofore known process, a plurality of molds arranged on trolleys placed one after the other are advanced through a tunnel vulcanizer which is steam heated. Unlike the first mold process, in this case a foam material which is emulsified with air and free of swelling agents is injected through particular holes provided on the cover until the whole volume of the mold is filled and fins of material overflow from proper openings of the mold to guarantee the appropriate dimension of the final product. Further steps of the process, i.e., opening of the molds and removal of the mattress, washing and lastly drying, are more or less the same as those of the first mold process.
It will be readily understood that the above-described mold processes require, to achieve certain dimensions for each product, a mold with corresponding dimensions. Therefore, if the width or height of the mattress is to be varied, it is necessary to plan and provide a new mold in order to satisfy the various market demands for different sized products.
Mold processes for manufacturing and marketing products with recesses, which are for the same use but have different dimensions, generally have a drawback in that they incur a high cost for their realization. Moreover, to implement such processes requires manual intervention by one or more operators, as, for instance, the removal of the mattress from the protuberances of the open mold with the negative consequence of damaging the products resulting from an excessive pull on a just-shaped spongy material and the great discomfort that the operator suffers from the significant heat emission resulting from the opening of the mold. Unfortunately, such mold processes furthermore result in cellular products with some flaws relative to the desired product. The cause of such product flaws is mainly connected to the vulcanizing step. In fact, to effect the vulcanizing step, it is necessary to utilize pressurized, very hot steam which is caused to circulate all around the mold along appropriate hollow spaces with consequent transfer of heat from the steam to the metallic masses of the mold, i.e., to the walls and protuberances of the mold. As the protuberances are numerous and are distributed in a regular manner in the foam mass, they transfer the vulcanization heat also to the product.
Unfortunately, the connections between protuberances and cover may give rise to an irregular cross-linking from one point to the other of the foam. This negative circumstance is due to the fact that each protuberance is associated with the cover through a metal plate that closes completely the inside of the protuberance to form a closed cavity. In some cases, the steam, due to its high pressure, is able to penetrate between the plate and the lateral wall of the protuberance to occupy at least partially a part of the cavity. Subsequently, at the end of the cycle, the steam deposits as a condensate and, as a consequence, the mold may have, in the vulcanizing step, either protuberances with empty cavities or protuberances whose cavities are partially filled with steam condensate.
It will be readily understood that the different heating conditions to which the different protuberances may be subjected can cause non-uniform cross-linking operations of the foam giving rise to a cellular product with characteristics different from one zone to the other. In these circumstances, the product, for instance a mattress, may exhibit during use the drawback of tearing in the zone which is less vulcanized as a result of numerous folding cycles of said zone.
Another process is known for manufacturing a layer of spongy material of unlimited length based on a technique of continuously rotating a steel tape between rollers forward the planar portion of the tape through a tunnel vulcanizer heated with high-pressure steam. At the entry of the planar portion of the tape, the foam material is injected and distributed in opposite senses to each other along a direction transverse to the advancing direction of the tape to form the desired thickness of the layer. After the vulcanization step, the foam layer is cut according to desired dimensions and then is passed through the usual washing and drying steps.
This continuous process could overcome some of the drawbacks cited in the above-described mold processes, i.e., either that of (1) obtaining products with different widths through suitable cutting operations transverse of the layer, (2) overcoming the numerous manual operations following the opening of the molds to remove the single products or (3) eliminating the discomfort experienced by the operators due to heat emission into the working ambient upon opening the molds.
However, it noted that this process is not suitable for manufacturing products with recesses in which, conventionally, the thicknesses of the foam can reach 20 cm and over.
In fact, the heat inside the steam tunnel can be used tor vulcanizing products with a low thickness, namely of several centimeters, but it is not sufficient for vulcanizing products with greater thicknesses. In substance, since this continuous process lacks the plurality of protuberances present in the molds of the mold processes described above and immersed in the surrounding foam mass to which the protuberances transfer vulcanization heat, the continuous process described above, which is based on the use of a steel tape, can be used only for manufacturing products without recesses with a thickness to a maximum of 5 cm, for instance, for plugs used for removing facial make-up and to be thrown away after use or to form possible upper and lower layers in a spring mattress. It is therefore readily understandable how this continuous process excludes the possibility of manufacturing products with recesses of latex foam, among other things mattresses with recesses having thicknesses between 14 and 18 cm, as for example mattresses of 14 cm thickness with cells having a depth of 11 cm.